The present invention relates generally to a plumb bob for mining applications and specifically to a plumb bob apparatus that can be used with laser surveying for accurately establishing directional headings in mining tunnels.
In conventional mining operations, it is desirable to ensure that mining tunnel headings are accurately maintained. If the headings of the mining tunnels are inaccurate, extra money is spent to compensate for the error and to regain the correct heading. Furthermore, if a number of tunnels are driven parallel to each other, the intervening unmined material forms support pillars. It may be necessary to provide these parallel tunnels at close distances, and thus a miscalculation in the accuracy of the headings may undermine the strength of the support pillars.
In usual mining operations, the headings of the tunnels are maintained by conventional surveying techniques which include placing a number of spads or hooks in the mine ceiling from which standard plumb bobs are suspended. The standard plumb bobs are used because they hang vertically, regardless of the direction of the surface to which they are attached. This process requires a team of people, which typically includes an engineer. The team uses a pair of standard plumb bobs suspended from spads such that they are perpendicular to the direction of the tunnel. The team uses a surveying device placed on a known location for determining positions of the standard plumb bobs. Once the positions of the standard plumb bobs are determined, the direction of the tunnel is calculated.
It is well known that this operation is inaccurate, time consuming, and expensive. In order to install the standard plumb bobs, holes are drilled into the ceiling of the mine, which can be 15 feet high. In order to drill the holes, the miners halt working and a machine, referred to as a Jumbo costing approximately $750,000, is used. A mine tractor is then used to hoist a miner to the ceiling to install plugs for the spads.
Recent advances have been made that reduce the costs involved in surveying a mine, as well as improving the accuracy of the surveys. Surveying equipment developed by Leica Geosystems AG, Switzerland (xe2x80x9cLeicaxe2x80x9d) provides for the rapid detection of the position of a target marking. The target marking is picked-up by imaging optics and a local opto-electronic detector of a theodolite or tachymeter. Electric signals from the detector are rapidly evaluated in a pre-processing unit by formation of sum functions for determining co-ordinates of the target marking.
In current mining applications, the target marking used is a prism. Equipment is brought into the mine to bore a hole in the wall in which to house the prism. The holes are numbered so that they may be used later as necessary. The Leica surveying equipment is used to automatically detect the location of the prisms, thus providing a simpler method for collecting data. As a result, it is often no longer required to have a separate team for calculating the co-ordinates, as the system can be used by the miners themselves.
The requirement to bore holes in the tunnel walls, however, introduces a new expense and step to the process. Equipment that was not previously required now has to be brought into the mine and used to bore the holes. Furthermore, it may be time consuming to bore the hole and place the prisms in the proper location.
Therefore, there is a need for an apparatus that makes it cheaper and simpler to place the prism in the desired location. It is an object of the present invention to obviate or mitigate the above mentioned disadvantages.
In accordance with an aspect of the invention there is provided a plumb bob apparatus. The plumb bob apparatus comprises a rigid surface mount member for coupling at a proximal end to a surface. The surface mount member is rotatable about its major axis. The plumb bob apparatus further includes a rigid device support member for pivotally coupling at a proximal end to a distal end of the surface mount member. When the plumb bob apparatus is coupled to a surface, the device support member will align vertically. The rigid device support member is also rotatable about its major axis. It is an advantage of the present invention that a plumb bob apparatus can be mounted on a substantially vertical surface.